Template Classes program example won't c

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Template Classes program example won't c

Template Classes program example won't compile

Hello everybody; I was doing a little program that I found in a programming book, just to practice a little, but I don't understand why it won't compile in my MS Visual Studio 2012. The error says: "error LNK1120: 6 unresolved externals".
I checked my code many times and now I'm out of ideas =/

Here is my code:
[NOTE: I'm aware that my method design is a little odd, but I did it this way because the template functions Problem(), Solution() and Congrats() used to be global template functions and I decided to change them into a template class.
Also, if you ask me "why do you print the answer 10 times?" my answer is: "why not?"]

// TemplatedMathProblem.h
#pragma once
#include <iostream>
using std::cout;
using std::endl;

template <class T>
class CTemplatedMathProblem
{
    private:
        // =====================================================================
        // Attributes
        // =====================================================================
        static char c_equals; // The '=' character
        char c_operand;       // The operator for the current problem
        T First;              // The 1st operand of the operation
        T Second;             // The 2nd operand of the operation
        T Answer;             // The user's answer
        T Result;             // The correct answer to the problem

        // =====================================================================
        // Private Methods
        // =====================================================================
        /* Display the arguments in the same order on the screen. Then it
        prompts the user to input the correct answer and, after that, it returns
        the input.
        */
        T Problem(T, char, T);

        /* It performs the desired operation between the first and second
        arguments in order to calculate the correct result of the problem. It
        returns the calculated correct answer.
        */
        T Solution(T, char, T);

        /* This function receives the correct answer and will display it
        alongside a congratulatory message 10 times.
        */
        void Congrats(T ans) {
            for (int i = 0; i < 10; i++)
                cout << ans << " CONGRATULATIONS! Correct answer!" << endl;
        }

    public:
        // =====================================================================
        // Public Methods
        // =====================================================================
        /* Display the mathematical problem on the screen and inputs the user's
         * answer
         */
        void DisplayProblem();

        /* Checks if the user's answer is correct and display a message 
        correspondingly
        */
        void CheckAnswer() const;

        // =====================================================================
        // Constructor & Destructor
        // =====================================================================
        /* Initialize the object's attributes with the values passed by argument
        */
        CTemplatedMathProblem(T, T, char op = '+');

        // Destructor
        virtual ~CTemplatedMathProblem() {}
};

// TemplatedMathProblem.cpp
#include "TemplatedMathProblem.h"
#include <iostream>
using std::cin;
using std::cout;
using std::endl;

// The '=' character
template <class T>
char CTemplatedMathProblem<T>::c_equals = '=';

// =============================================================================
// Constructor & Destructor
// =============================================================================
// Initialize the object's attributes with the values passed by argument
template <class T>
CTemplatedMathProblem<T>::CTemplatedMathProblem(T a, T b, char op):
c_operand(op), First(a), Second(b), Answer(), Result()
{}

// =============================================================================
// Private Methods
// =============================================================================
/* Display the arguments in the same order on the screen. Then it
prompts the user to input the correct answer and, after that, it returns
the input.
*/
template <class T>
T CTemplatedMathProblem<T>::Problem(T first, char operand, T second)
{
    bool b_inputIsValid; // flag that checks if the input is valid
    T answer;            // the user's answer

    // First, we display the problem
    cout << "Please solve the next problem: " << endl;
    cout << first << " " << operand << " " << second << c_equals << endl;

    // Then, we receive the input, checking that the input is a valid value
    do {
        cin >> answer;
        if (cin.fail()) {
            cout << "Sorry! Invalid input, please try again" << endl << endl;
            cin.clear();
            cin.sync();
            b_inputIsValid = false;
        }
        else
            b_inputIsValid = true;
    } while (!b_inputIsValid);

    // And finally, we return the answer
    return answer;
}

/* It performs the desired operation between the first and second
arguments in order to calculate the correct result of the problem. It
returns the calculated correct answer.
*/
template <class T>
T CTemplatedMathProblem<T>::Solution(T first, char operand, T second)
{
    T result; // The storage for the solution
    
    // We need to know which operation is in order to calculate the result
    switch (operand) {
        case '+': result = first + second; break;
        case '-': result = first - second; break;
        case '*': result = first * second; break;
        case '/': result = first / second; break;
        default: result = first + second; break;
    }

    // And we return the result
    return result;
}

// =============================================================================
// Public Methods
// =============================================================================
// Display the mathematical problem on the screen and inputs the user's answer  
template <class T>
void CTemplatedMathProblem<T>::DisplayProblem()
{
    Answer = Problem(First, c_operand, Second);
    Result = Solution(First, c_operand, Second);
}

// Checks if the user's answer is correct and display a message correspondingly
template <class T>
void CTemplatedMathProblem<T>::CheckAnswer() const
{
    if (Answer == Result) 
        Congrats();
    else
        cout << "Sorry, incorrect answer :(" << endl;
}

// main.cpp
#include <iostream>
using std::cin;
using std::cout;
using std::endl;

#include "TemplatedMathProblem.h"

int main()
{
    // The math problem
    CTemplatedMathProblem<int> Problem(10, 5);

    // We display the problem and input our answer
    Problem.DisplayProblem();
    Problem.CheckAnswer();

    // And we end the program
    cout << endl << "Press an key...";
    cin.sync();
    cin.get();
    return 0;
}

I hope you guys can help me =D

Last edited on

oldcrow (37)

For those who want to know the debugger's output and/or can UNDERSTAND it, I post it here for you:

1>  TemplatedMathProblem.cpp
1>  main.cpp
1>  Generating Code...
1>main.obj : error LNK2028: unresolved token (0A0003DC) "public: void __thiscall CTemplatedMathProblem<int>::DisplayProblem(void)" (?DisplayProblem@?$CTemplatedMathProblem@H@@$$FQAEXXZ) referenced in function "int __cdecl main(void)" (?main@@$$HYAHXZ)
1>main.obj : error LNK2028: unresolved token (0A0003DD) "public: void __thiscall CTemplatedMathProblem<int>::CheckAnswer(void)const " (?CheckAnswer@?$CTemplatedMathProblem@H@@$$FQBEXXZ) referenced in function "int __cdecl main(void)" (?main@@$$HYAHXZ)
1>main.obj : error LNK2028: unresolved token (0A0003DE) "public: __thiscall CTemplatedMathProblem<int>::CTemplatedMathProblem<int>(int,int,char)" (??0?$CTemplatedMathProblem@H@@$$FQAE@HHD@Z) referenced in function "int __cdecl main(void)" (?main@@$$HYAHXZ)
1>main.obj : error LNK2019: unresolved external symbol "public: __thiscall CTemplatedMathProblem<int>::CTemplatedMathProblem<int>(int,int,char)" (??0?$CTemplatedMathProblem@H@@$$FQAE@HHD@Z) referenced in function "int __cdecl main(void)" (?main@@$$HYAHXZ)
1>main.obj : error LNK2019: unresolved external symbol "public: void __thiscall CTemplatedMathProblem<int>::DisplayProblem(void)" (?DisplayProblem@?$CTemplatedMathProblem@H@@$$FQAEXXZ) referenced in function "int __cdecl main(void)" (?main@@$$HYAHXZ)
1>main.obj : error LNK2019: unresolved external symbol "public: void __thiscall CTemplatedMathProblem<int>::CheckAnswer(void)const " (?CheckAnswer@?$CTemplatedMathProblem@H@@$$FQBEXXZ) referenced in function "int __cdecl main(void)" (?main@@$$HYAHXZ)
1>C:\Users\XXX\Documents\Visual Studio 2012\Projects\Lessons\Lesson_12\Debug\Project1.exe : fatal error LNK1120: 6 unresolved externals

Last edited on

Cubbi (4774)

Templates go into the headers - move the contents of your TemplatedMathProblem.cpp into TemplatedMathProblem.h

oldcrow (37)

Oh, hahaha! Thanks man, very appreciated =)

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Template Classes program example won't compile